Calculating Miles Per Gallon

As the cost of gas goes up it becomes more and more important to use it more efficiently and therefore people become more interested in how much it is costing to drive a mile. It is relatively easy to calculate how many miles per gallon you are getting. Some cars actually calculate it for you as you are driving. But if yours doesn’t calculate the miles per gallon, you can easily do it yourself (although not “on the fly” as you are driving).

How to Calculate Miles Per Gallon

Simply fill up your gas tank (make sure it is full i.e. the pump shuts off) and write down the mileage from your odometer. Then the next time you fill up (make sure it is as full as it was the first time) and write down the number of gallons (from the gas pump) and the mileage again from your odometer.

Calculating Miles Per Gallon (mpg)

Now you have three numbers on your piece of paper, they are:

Miles at the start of the tank (first fill)

Miles at the end of the tank (second fill)

Gallons used

The formula for calculating Miles Per Gallon is simply miles driven divided by gallons used. So to calculate the miles driven you take the miles at the end of the tank and subtract the Miles at the start of the tank, and then you divide that by the total gallons of gas used.

Once you know your average miles per gallon (mpg), you can use our Cost of Gas per Month calculator to estimate how much you are spending on gasoline in an average month from this it will estimate your average cost of gas per year as well. By knowing how much you spend on gas you can get a better handle on your monthly commuting expenses and your overall budget.

If you get 34mpg and drive 1060 miles it would take you 31.2 gallons. The cost per gallon doesn’t have any bearing on this problem but the size of your tank does. Obviously, if you have a 35-gallon tank you would only have to fill up at home and once you arrive. But if you have a 16-gallon tank you would have to fill up once in the middle. Except you never want to get down to the last gallon so you would probably want to fill up twice.

When taking a trip I use the gas Buddy Trip App it not only tells you how many times you need to fill up it also calculates the best places to fill up (based on price) along the way. It even asks you what model car you are driving so it will know what size tank you have. You can find it here: https://www.gasbuddy.com/TripCostCalculator

You need to know how many miles per gallon your car gets. If your car gets 20 mpg and you drive 200 miles you might intuitively guess that you need 10 gallons but how do you figure that? Miles per gallon means miles divided by gallons which is commonly written as mpg but also can be written m/g. So the formula is m= (m/g)*g because the g’s cancel out. So if you want to know g you have to move the m/g to the other side of the equation. To do that you multiply both sides by g/m. So the new equation looks like this: (g/m)*m= (g/m)*(m/g)*g so you cancel (g/m)*m= (g/m)*(m/g)*g resulting in this (g/m)*m= g which is the same as m / (m/g).
So Gallons = miles divided by mpg. or 200 miles / 20 mpg = 10 gallons.

Brad, Tank size is irrelevant.
Total Cost / (cost/gal)= gallons
Gal x (Miles/Gal) = Miles
So in your case that would be:
$860.31 /$2 = 430.155 gal
430.155 x 15 = 6,452.325 miles
The key is to sort your units so they cancel out and remember if you divide you invert and multiply.

It always helps to sort out the units so you can find out the formula.

MPG could be written as m/g. So the units would be as follows: miles / (miles/gallon) = gallons.
Why? Invert and multiply. So miles / (miles/gallon) also equals miles x (gallons / miles)
Since you have one “miles” on top and one on bottom the miles cancel and you are left with gallons.